How to improve Power-On Reset?

[lpcware]

Content originally posted in LPCWare by Luis Digital on Sun May 06 14:06:42 MST 2012
Hello all,

I've noticed that 40% of the time the chips (LPC11xx) do not do a proper reset and left in an undefined state.

How to improve the POR without supervision hardware?

Or in the worst case using the reset pin as GPIO.

Maybe "brownout" is the key? :)
Edit: Now I noticed that the micro has to be working for BOD work. :(

Thank you.

[lpcware]

Content originally posted in LPCWare by gbm on Sun Aug 12 12:17:19 MST 2012
Or, you can remove the capacitor, diode, pull-up resistor and that 10 cm long PCB trace connected to the RESET pin to get the built-in POR circuit to work reliably, like I did in my over 20 LPC1xxx projects.

[lpcware]

Content originally posted in LPCWare by Luis Digital on Sat Aug 11 11:37:47 MST 2012
For the circuit to work properly, you need the capacitor and diode. END... I hope.

[lpcware]

Content originally posted in LPCWare by Luis Digital on Sat Aug 11 10:34:41 MST 2012
I have the same problem with my new board (LPC1764), and add pull-up does not solve the problem.

But I discovered the cause of the problem: [B]the capacitor is [/B][B]charged[/B].
The solution is to [B]add[/B][B] a diode from reset to VDD[/B], which discharge the capacitor when the circuit is off.

In my case the right solution is simpler to [B]remove the[/B][B]capacitor[/B].

Thank you all for your opinions.

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Tue May 08 17:14:37 MST 2012
And to avoid your 'undefined state' it's also a good idea to pullup ISP pin (PIO0.1) with 10k  :rolleyes:

Otherwise using this pin with your slow RESET can cause an ISP entry :eek:

[lpcware]

Content originally posted in LPCWare by NXP_Europe on Tue May 08 16:41:20 MST 2012
Hello Luis,

POR comes in at 'very' low Vdd and is not activated by an external reset, when the Vdd stays at e.g. 3V3.
BOD becomes active after building up the 3V3. When the Vdd drops, the BOD interrupt and BOD reset will become active under the programmed levels.

Zero is right, that you should add a pull up of appr. 10k ... 12k
You allready mounted the capacitor. This capacitor is used to keep the reset low for a short time, just after power up.

Let us know whether the problem (indefined state) is solved.

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Tue May 08 05:17:22 MST 2012
Without pullup RESET is incredible slow :eek:

This picture shows 2.5ms difference between RESET with 100nF cap and RESET with 100nF cap & 10k pullup.

RESET voltage: http://flic.kr/p/bUupLd

A simple 10k pullup without cap (that's what I use) is 3ms faster.

Note: LPCXpresso has a 12k pullup.

[lpcware]

Content originally posted in LPCWare by Polux rsv on Tue May 08 01:34:46 MST 2012

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Quote: Luis Digital
You mean "LPCXpresso is poorly designed"? :)
Oh, and that the POR of these chips is crap?

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In fact, my note was more related to your board.
And Zero wrote the same thing at the same time: Add a pullup resistor.

Angelo

[lpcware]

Content originally posted in LPCWare by Luis Digital on Mon May 07 13:18:02 MST 2012

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Quote: Polux rsv
Do you mean: "my LPC1110 board doesn't always start code execution properly due to poor power supply design/decoupling and no reset pull-up resistor" ???



Angelo

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You mean "LPCXpresso is poorly designed"? :)
Oh, and that the POR of these chips is crap?

[lpcware]

Content originally posted in LPCWare by Polux rsv on Mon May 07 08:41:09 MST 2012
Do you mean: "my LPC1110 board doesn't always start code execution properly due to poor power supply design/decoupling and no reset pull-up resistor" ???



Angelo

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Mon May 07 08:40:56 MST 2012
Add 10k Reset pullup :eek:

[lpcware]

Content originally posted in LPCWare by Luis Digital on Mon May 07 07:13:45 MST 2012
LPC1111 chip (Internal oscillator), for example: http://luisdigital.com/tienda/product.php?id_product=7

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Sun May 06 14:29:51 MST 2012

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Quote: Luis Digital
I've noticed that 40% of the time the chips (LPC11xx) do not do a proper reset and left in an undefined state.

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Can't follow you :confused: Which hardware are we talking about :confused: